1. Field of the Invention
This invention concerns improvements in and relating to water heating apparatus for use in any type of application, domestic, industrial or other. More particularly the invention is concerned with such apparatus which uses the medium of the water for the heating effect of the electric current, for example, by means of uninsulated electrodes immersed in the water.
2. Prior Art
A large amount of water heating is done by means of thermostat controlled electric heating of the water in a drum, certainly in domestic applications a vast majority of cases. This allows the water to be heated slowly by a relatively low capacity heater and stored at the required temperature in the drum from which it can be drawn from time to time. The serious disadvantage is very poor efficiency of this system due to heat loss from the drum since the water is held at a high temperature largely continuously. Despite this disadvantage this system is adopted widely probably because it is technically simple and inexpensive and the electrical power demand is relatively low albeit for long periods.
Demand water heaters are in use on a smaller scale where the elements heat only when a flow of water through the apparatus is initiated requiring relatively high electrical power supply levels if a strong flow of very hot water is to be supplied. The performance of such heaters is moreover vitally affected by the conductivity of the water which varies to a remarkable degree from place to place and from time to time. So much so that fixed design demand heaters are likely to give unsatisfactory performance in many instances. Reference is made to Table A which shows the extreme range, for example, from as low as 1 millisiemes at a Swartruggens minimum to 993 millisiemens at a Britstown maximum. The table shows that not only is the range extreme from place to place but also in many individual places.
Table B shows that categorising results on a regional basis does not introduce any uniformity which would permit supplying apparatus specially adapted to suit each region.
Some designs have been proposed which include electrodes moveable in respect of the water to allow adjustment to compensate for variations in conductivity. It would seem that these designs, however, have not been successful probably because of high cost and low reliability as well as the difficulty that the average user especially, for example, in the domestic context cannot be relied on to make suitable adjustments especially when the conductivity of water in a single area swings between wide limits as Table A shows. Automated controls for servo motor actuated adjustment have not been seriously proposed certainly not in the domestic context, for example.
The "Electrical Engineer's Handbook" 1973 Ed., publ. Butterworth, at page 14-55 says: ". . . variation in water resistivity (which can be allowed for in large installations) makes mass production for domestic use very difficult." The "Electrical Engineer's Reference Book" publ. G. Newnes Ltd., at page 15-24 says: ". . . the great variation that one may expect in the resistivity of water supplies which while it can be easily allowed for in designing specific high-loading installations, presents an almost insuperable difficulty to mass productions for general domestic use." No solution for these problems is offered.
TABLE A ______________________________________ Av. Min. Max. Mean Median ______________________________________ 1541 Kommando Drift, EP 10,9 85,9 55,3 33 1620 King Williams Town, 25,0 83,6 52 50 EP 1730 Queenstown, EP 2 26 10 8 1850 Umzinkulu, Natal 22 46 32 38 1920 Pmburg, Natal 5 20 7 7 1182 Uniondale, SW Cape 14 58 22 18 1210 Uitenhage, EP 15 23 19 20 1323 Waterford, EP 5 550 158 154 1430 Grahamstown, EP 43 136 90 100 1513 Stennsburg, EP 21 81 32 23 0911 Laingsburg, Karoo 35 130 70 65 0925 Calitzdorp, Karoo 9 53 30 42 1010 Mossel Bay, SW 72 227 139 176 Cape 1090 Humansdorp, EP 18 28 23 24 1130 Willowmore, EP 25 850 298 273 2010 Bergville, Natal 4 17 8 7 2030 Newcastle, Natalo 7 39 17 13 2113 Eshowe, Natal 15 26 20 22 2144 Pongola, Natal 6 114 40 95 2154 Ermelo, E. Tvl 4 10 5 4 0121 Pretoria, Tvl 15 69 45 52 0130 Swaartruggers 1 49 19 9 0140 Nylstroom, N. Tvl 5 8 6 5 0150 Potgietersrus, N. Tvl 3 37 11 15 0160 Pietersrburg, N. Tvl 5 21 8 7 0180 Louis Trichardt, 10 44 22 15 N. Tvl 0190 Parfuri, N. Tvl 5 55 21 17 0232 Groblersdaal, N. Tvl 6 38 21 16 0280 Duiwelskloof, N. Tvl 3 13 5 6 0312 Villiers, OFS 10 31 18 15 0390 Christiana, Tvl 11 127 52 77 0323 Potchefstroom, Tvl 17 79 51 59 0352 Bloemfontein, OFS 16 52 29 37 0420 Weppenaar, OFS 10 38 19 23 0434 Colesburg, Karoo 10 28 16 17 0460 Britstown, Cape 58 993 352 329 0510 ClanWilliam, W. 1 14 8 9 Cape 0710 Malmsbury, W. Cape 2 52 13 11 0740 Caledon, W. Cape 8 12 9 9 0810 Worcester, W. Cape 4 15 7 6 0840 Robertson, W. Cape 6 17 10 7 Jhb. 35 Read's borehole 17 Lowest 1 8 5 4 Highest 58 993 352 329 ______________________________________
TABLE B __________________________________________________________________________ S.W. E. N. W. N. W. E.P. Natal Cape Karoo Tvl. Tvl. Tvl. OFS Cape Cape __________________________________________________________________________ 33 38 18 65 4 52 9 15 329 9 50 7 176 42 16 5 77 37 11 8 7 17 15 59 23 6 13 7 20 22 7 154 95 15 100 17 23 6 24 273 Av. 46 76 30 97 41 10 16 48 24 109 8 High 273 95 176 65 16 52 77 37 329 11 Low 8 7 18 17 4 5 9 15 -- 6 __________________________________________________________________________
It is an object of this invention to provide water heating means by the heating effect of electric current flow in the water which is capable of compensating for wide water conductivity ranges, for example of the extent indicated above.
It is a further object to do this in a practical solution, thus without moving parts which can be subject to wear, sticking or other unreliability or poor durability.